Parkinson's disease is chemically induced by infusion of MPTP into the right internal carotid artery of an animal. The infusion produces injury to one side of the brain, causing Parkinson symptoms and spontaneous motor activity of circling toward the injured side. Treatment with drugs (apomorphine or L-DOPA/ carbidopa) or brain implants causes circling towards the intact side. An automated method to measure this circling as a function has been developed. The rotation of the animal is plotted as a bar graph as function of time. The previous method of monitoring animals by means of television was both time consuming and expensive, especially with multiple animal experiments. The system consists of back-pack-mounted infra-red (IR) emitting transmitters, cage mounted IR sensors, specialized electronics and a microcomputer system capable of monitoring many animals simultaneously. Each IR transmitter consists of an oscillator pulsing four IR light emitting diodes (LED), mounted on a 9 volt transistor radio battery and inserted in a jacket worn by the animal. A radiation pattern of 180 degrees is achieved by the transmitter. An IR phototransistor is the receiver, and it is mounted in the center of each cage wall. The output of each detector is amplified by a high pass amplifier, full wave rectified, processed by a slow time constant low pass filter and then presented to a 32 channel A/D converter located in a Zenigh Z-100 PC computer system.